This invention relates to a process and a mechanism for the automatic manufacturing of articles made from plastic, particularly recyclable plastic waste. The mechanism comprises several stationary divided compression molds flanged to a plasticizer. Each of the divided compression molds is locked in a closed position during the process. The locking function allows for a tight closing of the flanged divided molds.
The processing of the plastic material takes place in a plasticizer which may be constructed as a screw-type extruding machine or as a roller-type extruding machine. The weight of the very viscous melting is determined with respect to the size of the object to be molded and then the melting is pressed in a mold. In another arrangement constructed for this purpose, the melting may also be filled directly from the plasticizer into a mold, in which case a sensor can measure the filling pressure in order to ensure that the mold is filled.
In order to let the plasticizer operate continuously, a separator head is connected and disconnected sequential to each of the several molds by means of an inlet shut-off mechanism. Nevertheless, a considerable number of operating sequences are necessary which must be carried out manually and which therefore result in considerable expenditures.
A locking and opening mechanism for a plastics mold is disclosed in the European Patent Document 0 221 872 A2. There a hydraulic cylinder pivotedly arranged on a lower mold half to lift off the upper mold half, whereby the opening and closing of the plastics mold is achieved. Another hydraulic cylinder, which is disposed on the upper mold half, is articulated with a double-armed lever which is rotatably disposed on the upper mold half. The lever carries a disk-shaped closing body on its other free end. This closing body extends behind a projection, which is fixedly connected with the lower mold half, whereby the plastics mold can be locked in the closed position.
The closing motion of the mold can be stopped by means of a limit switch. This mechanism can only be used for plastics molds of fairly small dimensions. In the case of larger molds, a lifting-off of the upper mold must have as horizontal a movement as possible to avoid damage to the molded article. This is true during the removal from the mold as well as during the tightening of the locking mechanism in order to withstand the high filling pressure of the mold.
The U.S. Patent Document U.S. Pat. No. 4,643,663 describes a divided mold, wherein the movable mold half is brought into a closing or emptying position by means of one or several hydraulic cylinders. However, a locking and tightening of the locking is not provided. Hence that arrangement is not suitable for large molds filled with recyclable plastics.
In contrast, European Patent Document EU-PS 381 770 A1 shows a mold where the movable mold half is brought into its open and closed positions by four threaded spindles which correspond with an equal number of lift nuts which are rotatably but vertically unshiftingly disposed in the movable mold half and which are driven synchronously by a gear motor. Here there is no locking and no tightening of the two mold halves so that this construction is also not suitable for the manufacturing of large-surface articles made of recyclable plastics.
It is an object of the invention to let all operating sequences--from the processing of the plastic material by means of the plasticizer, to the ejection of finished molded object--occur automatically in order to produce low-cost articles because of an efficient utilization of the mechanism. Also when used with large molds, the mold is a lockable in a tightenable manner in the closed position.
This object is achieved by means of the following sequence of process steps:
a) Mold release and indication of the readiness to be filled; PA1 b) Opening of the locking mechanism on the separator head assigned to the mold; PA1 c) Filling of the mold and refilling of a plunger device, which filling is indicated by filling pressure monitoring; PA1 d) Closing of the locking mechanism on the separator head; PA1 e) Subsequent pressing of additional melting into the mold by means of the plunger device; PA1 f) Cooling of the mold; PA1 g) Opening of the mold cover and removing the molding; and PA1 h) Closing of the mold cover, locking, tightening and switching on the heater. PA1 a) The separator head may be lengthened in a linearly elongated manner; PA1 b) the intermediate pieces between the inlets and the plasticizer may be heatable by means of an additional heater; and PA1 c) the plasticizer may be constructed as a screw-type extrusion machine or as a roller-type extrusion machine.
Several stationary molds can be connected to a separator head which is preferably flanged to the plasticizer. A shut-off mechanism is connected between the separator head and the mold.
The mold release and the filling readiness may be initiated by a pressure monitoring sensor which causes the opening of the inlet shut-off mechanism connected with the mold. The melting can then flow from the separator head directly into the corresponding mold. A plunger device which is arranged oppositely to the inflow opening of the mold may also fill up after the filling of the mold. The sensor monitors the filling pressure and cause the closing of the inlet shut-off mechanism as soon as the desired pressure is reached. However, at the same time, another inlet shut-off mechanism on the separator head leading to another mold is opened so that no delay occurs in the continuous ejection of the melting by the plasticizer.
As soon as the inlet shut-off mechanism of the latter, already filled, mold is closed, the additional pressing of melting into the mold, which is caused by the sensor, can take place by means of the plunger device. The pressing of melting into an already filled mold has the advantage that complicated molds, such as molds which tend to have bubbles or otherwise not completely filled contours of the articles, are filled in a perfected manner. The rate of rejections is reduced considerably.
In addition, the switching-on of the cooling device for the mold, may be carried out by a signal of the sensor. The mold can be emptied earlier if it is cooled. The cooling and intermediate heating of the mold may take place several times consecutively by means of the switching on and off of the corresponding heating and cooling devices. This has the advantage that the removal from the mold can take place in an easier and simpler manner.
In addition, the opening of the mold may take place within a predetermined time interval by means of a control device and the molding may be removed from the mold at the same time.
The molding may be ejected onto a conveyor belt, which is not shown, and may be transported away.
In addition, the closing of the mold cover and the intermediate heating of the mold may be caused by a signal of the control device. A sensor may signal the readiness of the emptied mold to be filled.
The mechanism for carrying out the process comprises a plasticizer, a separator head with several blockable inlets to the individual molds, with one afterpressing device for each mold for the adding of additional melting to the individual molds.
The possibility therefore exists of also transporting the prepared melting along a longer path to the individual molds and to therefore connect a plurality number of molds to one separator head.
In addition, a melting delivery pump may be connected between the plasticizer and the separator head. A pressure of approximately 400 bar will sometimes be required, for a complete filling of the mold with melting, in the case of a separator head which is linearly lengthened in the manner of a strand and has several individual molds flanged to it. Here a melting delivery pump may be constructed as a gear pump. At the end of the separator head, which is linearly lengthened in the manner of a strand, a pressure of approximately 100 bar is still required for the filling of the mold. The end of the separator head may be closed off by means of a shut-off mechanism which, if required, may be switched to a flow-through position, should there be a disturbance in the course of the manufacture.
In addition, the shut-off mechanism may be constructed as an electrically actuated rotary disk valve, or may also be designed as a needle shut-off nozzle. These two shut-off devices have been successful in practice. However, the shut-off mechanism may also be constructed as an electrically or hydraulically operable shut-off slide valve.
Furthermore, the molds may form a unit with the pertaining shut-off mechanism and may be flanged to the linearly elongated separator head. A compact construction may be achieved in this manner.
In an advantageous development of the invention, a plunger device for a subsequent pressing of additional melting into the mold may be arranged on every mold. This plunger device is arranged diametrically with respect to the inlet opening for the melting on every mold and has the result that, after the desired filling pressure in the mold has been reached and the inlet shut-off mechanism is then shut, a predetermined amount of melting is then additionally pressed into the mold in order to compensate for possible bubbles or incompletely filled contours of the molding, particularly in the case of fairly large and complicated molds. The plunger devices fill with melting which has flown through the mold and are caused by a sensor to press this melting back into the mold in a recirculating manner.
In addition, a controllable heating and cooling device may be connected to every mold. During the cooling operation, this device is frequently connected and switched on. This not only accelerates the cooling operation but also considerably facilitates the removal from the mold.
Also, the intermediate pieces between the outlets on the separator head may have an additional heater. As a result, heat losses are compensated in the case of the flow through the separator head to the molds arranged at the end of this separator head, which is linearly lengthened in the manner of a strand.
In addition, the molds may be equipped with a sensor which closes the shut-off mechanism when the desired pressure is reached in the mold.
A control device may be arranged for each mold which causes the subsequent pressing of additional melting into the already filled mold.
In addition, the control device can switch the heater to cooling in a time-staggered manner and, after a certain time interval, may cause the opening of the mold cover and the removal of the molding from the mold. In this case, the moldings may be ejected onto a conveyor belt or may be removed manually.
Furthermore, the control device may cause the closing of the mold cover. The opening and closing may take place hydraulically.
In addition, the control device may signal the release of a molded product and the closing of the mold at the inlet shut-off mechanism. By means of a preprogrammed control sequence, the emptied and closed mold may again be included in the operating cycle. The automatic sensor monitoring device reports to the control device when a mold is free for filling. Each of the molds may be designed differently, and the plasticizer should have a capacity of approximately 200 to 250 kg/h.
Another mechanism for carrying out this process comprises a plasticizer, a separator head with several inlet shut-off mechanism for the individual molds. The molds are equipped with one heating and cooling device respectively and one afterpressing device respectively for the subsequent filling of additional melting into the individual molds.
In order to reduce the length of the arrangement and to avoid a cooling of the melting in an excessively extended separator head, the separator head, particularly in the case of smaller individual molds, may have a circular construction. There, each of the molds with their inlet shut-off mechanism are flanged to the separator head in a star-shaped manner.
A mechanism for the automatically closing, locking and tightening as well as opening of the divided mold is provided by a programmable central control. The mold is in two pieces--a firmly anchored lower mold half in a lower supporting frame and an upper movable mold half arranged in an upper supporting frame. Opening and closing of the mold takes place in the perpendicular direction. This mechanism is more advantageous for the removal of the molded article from the mold.
Furthermore, a yoke bridge or at least a threaded spindle may be fastened to the lower supporting frame. The yoke bridge is used for accommodating a working cylinder or lift nuts for the moving of the upper supporting frame which supports the movable mold half. If the threaded spindles are fastened to the lower supporting frame, the lift nuts are installed in the movable mold half or are installed in the upper supporting frame. The lift nuts are rotatably but vertically unshiftingly disposed in the above-mentioned parts and are synchronously driven by a gear motor.
However, the threaded spindles may also be fixedly connected with the upper supporting frame. Here, the lift nuts are rotatably but vertically unshiftingly disposed in the yoke bridge and are driven synchronously by a gear motor.
The gear motor or the operating cylinder may be shut-off by a stop switch. In order to ensure a certain contact pressure in the end positions of the closing and emptying position, the gear motor may be equipped with a torque coupling.
Moreover, the locking elements may mesh in tightening devices when the mold halves are closed, whereby the two closed mold halves become firmly locked and braced with respect to one another.
The locking elements can be actuated by one or more hydraulic cylinders or by a lever arrangement. The operation of the actuators can be automatically controlled and coordinated with the mold coolers so that the degree of cooling of the filled mold can be determined.
The moveable supporting frame together with the upper movable mold may slide in a guide way attached to the mold frame. This provides necessary meshing accuracy between the mold halves in the closed position.
The locking elements may be tightened by means of tightening devices arranged on the movable mold half. The tightening devices may consist of eccentric shafts moved by a hydraulic cylinder.
Locking bolts may be arranged on the upper mold half. The locking bolts may have semicircular recesses for cooperation with locking mechanism of the lower mold half or the mold frame.
Hydraulically rotatable locking shafts may be arranged on the lower mold half. The locking shafts may have milled-out recesses which correspond to the recesses in the locking bolts. A locking of the two mold halves as well as a tightening of the locking can also be achieved by means of this mechanism.
Alternatively, the locking bolts may have a ring groove in an end area that cooperates with a slidably arranged locking frame disposed on the lower mold half or on the lower supporting frame. This locking frame can be operable either hydraulically or pneumatically. The locking frame has bores which correspond to the locking bolts and which are expanded to form oblong holes. The expanded oblong hole portion being smaller in its inner width than the bore. By shifting of the locking frame when the mold halves are closed, the lateral portions of the narrower oblong hole engage the ring grooves of the locking bolts. By means of a slanting of the lateral portions of the oblong holes engaging in the ring grooves, a tensioning of the two mold halves may be achieved.
According to another embodiment, grooves, preferably in a ring shape, may be arranged in the area of the mold seam of the two mold halves. This grooves become narrower toward the inside of the mold and reach over the mold seam. Links, which have the same geometrical shape as the grooves, can be moved in and out of these grooves by means of a moving element. The moving element may be operated hydraulically, pneumatically or mechanically by way of an eccentric lever or by way of a toggle joint. As a result, it is possible to control the locking elements from a central control. The flanks of the groove may narrow down by a central angle of approximately 14.degree.. With a bipartition angle of approximately 7.degree., the selflocking will stop so that the link will not bind in the groove and can be easily moved. The link itself may also be conically formed in the same central angle, specifically on the outer contour of the conical part. This allows for tightening of the connection of the two mold parts.
Also, a feed head and a cut-off slide may be arranged on the lower mold half. This has the advantage that when the inlet filling valve is closed, the melting, which is subjected to a high filling pressure, cannot continue to flow and lead to disturbances during the subsequent filling operation.
Finally, the timing of the drive assemblies can be controlled from the central control.
Naturally, a fully automatic operation of the system also includes the automatic removal of molded articles from the mold. The articles removed from the mold can be ejected to a conveyor belt which is not shown.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.